$(function(){
	    /**生成一个随机数**/
	    function randomNum(min, max) {
	        return Math.floor(Math.random() * (max - min) + min);
	    }
	    /**生成一个随机色**/
	    function randomColor(min, max) {
	        var r = randomNum(min, max);
	        var g = randomNum(min, max);
	        var b= randomNum(min, max);
	        return "rgb(" + r + "," + g + "," + b + ")";
	    }
	    var code=drawPic();
	    document.getElementById("changeImg").onclick = function(e) {
	        e.preventDefault();
	        code=drawPic();
	    }

	    //表单提交事件
	    // $("form").submit(function (e) {
        //     if($("#vercation").val().toLowerCase() !== code.toLowerCase()) {
        //         $("#vercation").css("borderColor","red");
            //         e.preventDefault();
        //     }
        // })
	    /**绘制验证码图片**/
	    function drawPic() {
	        var canvas = document.getElementById("canvas");
	        var width = canvas.width;
	        var height = canvas.height;
	        //获取该canvas的2D绘图环境 
	        var ctx = canvas.getContext('2d'); 
	        ctx.textBaseline ='bottom';
	        /**绘制背景色**/
	        ctx.fillStyle = randomColor(180,240);
	        //颜色若太深可能导致看不清
	        ctx.fillRect(0,0,width,height);
	        /**绘制文字**/
	        var str ='ABCEFGHJKLMNPQRSTWXY123456789';
	
	　　　　 var code="";
	　　　　　//生成四个验证码
	        for(var i=1;i<=4;i++) {
	            var txt = str[randomNum(0,str.length)];
	            code=code+txt;
	            ctx.fillStyle = randomColor(50,160);
	            //随机生成字体颜色
	            ctx.font = randomNum(15,40) +'px SimHei';
	            //随机生成字体大小
	            var x =10 +i *25;
	            var y = randomNum(25,35);
	            var deg = randomNum(-45,45);
	            //修改坐标原点和旋转角度
	            ctx.translate(x, y); 
	            ctx.rotate(deg * Math.PI /180); 
	            ctx.fillText(txt,0,0);
	            //恢复坐标原点和旋转角度
	            ctx.rotate(-deg * Math.PI /180);
	            ctx.translate(-x, -y);
	        }
	        
	        /**绘制干扰线**/
	        for(var i=0;i<3;i++) {
	            ctx.strokeStyle = randomColor(40, 180);
	            ctx.beginPath();
	            ctx.moveTo(randomNum(0,width/2), randomNum(0,height/2));
	            ctx.lineTo(randomNum(0,width/2), randomNum(0,height));
	            ctx.stroke();
	        }
	        /**绘制干扰点**/
	        for(var i=0;i <50;i++) {
	            ctx.fillStyle = randomColor(255);
	            ctx.beginPath();
	            ctx.arc(randomNum(0, width), randomNum(0, height),1,0,2* Math.PI);
	            ctx.fill();
	        }
	        return code;
	    }
})